Many hollow or dished objects are formed from a sheet of metal by deep drawing or stamping in a press. For example, many parts employed in the aeronautical and automotive industries are made by such processes. In operations of this type, it is necessary to apply a lubricant to the metal sheet to enhance the drawing operation and reduce wear on the tool and die. Sheet lubricators thus are well known and comprise generally driven opposed rollers of felt or the like which apply the lubricant from a circulating supply thereof and driven opposed squeeze rollers, of metal, designed to remove the excess lubricant.
In a typical sheet metal operation of the type under consideration, a supply of blank metal sheets is stacked on a table where an operator is stationed. That operator removes the top sheet from the stack and feeds it into the lubricator positioned nearby. The metal sheet is driven through the lubricator and exits at the opposite end thereof where it must be taken up by a second operator who then places it into the press for the stamping operation. In some instances, the added expense of the second operator and the attendant loss of floor space renders the cost of the entire operation competitively prohibitive.
The type of problem alluded to can be generally characterized as one of material handling efficiency and is by no means unique to the sheet metal art. On the other hand, examination of the known prior art in this field reveals that the proposed solutions invariably are precisely tailored to the particular material and operation involved. Those prior proposals thus have limited applicability and little, if any, utility in the particular sheet metal operations with which the invention is concerned.
Representative examples of prior art conveyor-material handling systems designed to deal with specialized problems are U.S. Pat. Nos. 3,251,450 which teaches apparatus for transferring bakery pans from one conveyor to a second, transverse conveyor; 3,844,402 which teaches a conveyor system with a rotatable carrying plate for depositing fermented dough products; 3,137,396 which teaches an elaborate system for transporting tobacco products; 1,597,961 which teaches an apparatus for delivering empty pallets to a molded brick dumper; 2,795,312 which teaches a mechanism for switching a flow of lapped articles such as newspapers from one conveyor to another; 3,863,912 which teaches a paper document feeder for a copying machine; and 3,789,973 which teaches a multiple endless belt system for feeding highly flexible workpiece sheets into a tool and extracting it therefrom. The unsuitability of those prior art systems for dealing with the particular problems of the character described here will be apparent to those skilled in the art of sheet metal lubricators and metal drawing operations.
Other prior art conveyor-material handling systems are likewise characterized by a variety of disadvantageous features. Thus, for example, U.S. Pat. No. 2,669,263 teaches a mechanism for returning to a worker a board or piece of lumber after the same has been sawed by a rip saw. In that device, the relatively heavy and rigid board is conveyed by driven rollers up an incline to the return station. That conveyor mechanism obviously would be ineffective for the slippery, lubricated, relatively light and flexible sheet with which this invention is concerned. In addition, the patented device employs sprocket wheels and chains which are objectionable for a number of reasons including worker safety.
In U.S. Pat. No. 1,767,574, there is disclosed a wheeled device positionable for catching hot metal plates as they are ejected from a mill. That device includes a complex system with a reversible motor, gears, driven conveyor wheels and a tiltable table for returning the plate to the mill for re-rolling, or conveying it to a stacking station. Again, the patented device is incapable of efficiently and inexpensively returning a lubricated metal sheet to the same operator.
Still another type of conveyor-material handling apparatus is disclosed in U.S. Pat. No. 3,392,813 which comprises an upper, inclined gravity conveyor section for storing a supply of empty tote pans, a lower gravity conveyor section for storing filled tote pans and a connecting gravity conveyor section pivotal between the two storage sections. The pivotal section is retained in the upper aligned position by magnets and pivots to the lower aligned position only after a tote pan positioned thereon has been filled with merchandise, presumably by an operator positioned there. That apparatus is unsuitable for the sheet metal lubricator applications here involved because it depends for its operation on an increase in weight of the conveyed piece.
From the foregoing discussion of the prior art, it is apparent that there exists a need for an inexpensive, simple and positive acting feed and return system for sheet metal lubricators that enables a single, stationary operator to conveniently, efficiently and safely lubricate a sheet and regain the lubricated sheet for placement in the press for the drawing operation.